JP2006177178A - Control device for cylinder direct injection type spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve both drastic delay of ignition timing and combustion stability and to realize rise in exhaust gas temperature and reduction in HC emission amount when an engine is cold. <P>SOLUTION: In a warming up completion state where the temperature of cooling water exceeds 80°C, regular stratified combustion operation and homogeneous combustion operation are performed. In a cold engine state where the temperature of the cooling water is below 80°C, to promote activation of a catalytic converter and to reduce HC emission amount, a top dead center injection operation mode is performed, and fuel injection is performed astride a compression top dead center, such that injection start timing ITS comes before the top dead center and injection completion timing ITE comes after the top dead center. Ignition timing ADV comes after the top dead center. At the compression top dead center, swirls and tumbles are attenuated, minute turbulence actively occurs, and change in a piston position is small. Therefore, stable combustion can be realized. Ignition timing is corrected based on the temperature of the cooling water and comes advance side as the temperature lowers so as to secure combustion stability and generated torque with respect to friction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an in-cylinder direct injection spark ignition internal combustion engine that directly injects fuel into a cylinder, and more particularly to control of the injection timing and ignition timing.

Patent Document 1 discloses that when an exhaust purification catalytic converter is in an unwarmed state lower than an activation temperature, fuel is injected during the compression stroke, and the ignition timing is retarded from the compression top dead center. Technology is disclosed.
JP 2001-336467 A

  In order to raise the exhaust gas temperature and reduce HC in order to achieve early activation of the catalyst when the internal combustion engine is cold, it is desirable to retard the ignition timing as much as possible, but if the ignition timing is significantly retarded Since the combustion stability deteriorates, it cannot be retarded from a certain limit determined from the viewpoint of combustion stability. In the conventional technique such as Patent Document 1, it is difficult to ensure stable combustion, particularly under conditions such as cold, and the retard limit of the ignition timing determined from the combustion stability is relatively advanced, which is sufficient. The ignition timing delay cannot be realized.

  The present invention provides a control device for an in-cylinder direct injection spark ignition internal combustion engine that includes a fuel injection valve that directly injects fuel into a cylinder and that includes an ignition plug. When it is necessary to raise the exhaust gas temperature, the fuel injection is performed as the top dead center injection operation mode so that the injection start timing is before the compression top dead center and the injection end timing is after the compression top dead center. The ignition is performed in a period straddling the compression top dead center, and ignition is performed after the compression top dead center delayed from the injection start timing. In particular, the ignition timing is set according to the engine temperature.

  FIG. 1 illustrates the fuel injection period and ignition timing in the top dead center injection operation mode of the present invention together with the change in the in-cylinder pressure. The injection start timing ITS is before the compression top dead center (TDC), and the injection end timing ITE is After compression top dead center (TDC). The length of the injection period T during that time corresponds to the injection amount. The ignition timing ADV is after compression top dead center (TDC), and is a timing delayed by a predetermined crank angle (for example, 10 ° CA to 25 ° CA) from the injection start timing ITS. This delay period D generally correlates with the distance from the fuel injection valve to the spark plug.

  The injection start timing ITS and the injection end timing ITE are controlled so that the period before the compression top dead center in the first half and the period after the compression top dead center in the second half are substantially equal with the compression top dead center (TDC) as the center. You may make it do.

  FIG. 2 shows the piston position change amount and the combustion chamber volume change amount due to the piston stroke in one cycle of the internal combustion engine. As shown in the figure, the amount of change per unit crank angle is the largest near the middle position of the stroke, and is very small near the bottom dead center (BDC) and near the top dead center (TDC). Therefore, in the vicinity of the compression top dead center where the fuel injection is performed in the present invention, the piston position change and volume change are very small, and a stable field that is not affected by the piston movement or the like can be formed.

  In the cylinder, a relatively large gas flow such as a swirl flow or a tumble flow is generated in the intake stroke and remains in the compression stroke. However, a large flow such as a swirl flow or a tumble flow is When the piston reaches near the compression top dead center and the combustion chamber becomes narrow, it collapses rapidly. FIG. 3 shows a change in flow velocity of a large flow in the combustion chamber under various engine speeds. As shown in the figure, a swirl flow or a tumble flow having a strength corresponding to the rotation speed is generated. Collapses rapidly before reaching compression top dead center (360 ° CA). Therefore, in the present invention, the fuel spray injected near the compression top dead center is not moved by a large flow such as a swirl flow or a tumble flow, and always forms a spray in a stable manner on the spark plug. Is possible.

  On the other hand, the energy of a relatively large flow such as the swirl flow or the tumble flow described above transitions to minute turbulence as the flow collapses. Therefore, the minute disturbance in the combustion chamber increases rapidly just before the compression top dead center. FIG. 4 shows the intensity of the minute turbulence caused by the collapse of the flow shown in FIG. 3 as a so-called turbulent flow rate converted to a flow velocity, and as shown in the figure, immediately before the compression top dead center. , Disturbances increase greatly. Such minute disturbances contribute to the activation of the combustion field, and a combustion improving action is obtained.

  In other words, the field in the combustion chamber near the compression top dead center where the fuel is injected does not have a large flow that moves the spray, and there are many minute disturbances that activate the combustion, It is a very stable place against the movement of the piston. Therefore, stable combustion is possible with the ignition timing retarded from the compression top dead center, and the retard limit of the ignition timing that is limited in terms of combustion stability is on the retard side. For this reason, the exhaust gas temperature can be significantly increased by a large retardation of the ignition timing, and the HC emission amount is reduced.

  Here, the above-mentioned combustion stability correlates with the engine temperature and basically tends to deteriorate as the engine temperature is lower.

  Further, in the top dead center injection operation mode in which the ignition timing is greatly retarded as described above, the generated torque is relatively small for the same fuel amount and intake air amount. When the engine in which the injection operation mode is generally performed is cold, the friction of each part of the engine is larger than that after warming up, so the torque that can overcome the friction and allow the engine to operate independently (stall limit torque) There may be cases where it cannot be obtained. In other words, the internal combustion engine may stop due to a factor different from combustion instability. The above friction correlates with the engine temperature.

  Therefore, in the present invention, the ignition timing in the top dead center injection operation mode is set according to the engine temperature.

  In one aspect of the present invention, the ignition timing is set according to the engine temperature so that the combustion stability is equal to or higher than a predetermined combustion stability. In other words, combustion in the top dead center injection operation mode promotes afterburning, so that combustion stability tends to be lower than normal combustion and there is a problem of instability of combustion, but combustion stability is Basically, it is bad when the engine temperature is low, such as immediately after a cold start, and the combustion stability is relatively improved if the engine temperature such as the combustion chamber wall temperature is high. Therefore, by setting the ignition timing in accordance with the engine temperature, it is possible to set the ignition timing to a more retarded side while ensuring combustion stability.

  In one aspect of the present invention, the ignition timing is set according to the engine temperature so that the generated torque exceeds the stall limit torque that varies with temperature. The lower the engine temperature, the greater the friction, and the higher the torque that can be operated independently without stalling, that is, the stall limit torque, but the ignition timing is advanced even in the top dead center injection operation mode with the same fuel amount. When corrected, the generated torque increases. Therefore, by setting the ignition timing in accordance with the engine temperature so as to exceed the stall limit torque, stall or rotation fluctuation due to friction can be reliably avoided.

  Further, in one aspect of the present invention, the first ignition timing obtained according to the engine temperature and the stall limit torque that changes depending on the temperature are set so that the combustion stability is equal to or higher than a predetermined combustion stability. The second ignition timing obtained according to the engine temperature is compared so as to exceed the value, and the advance side value is set as the ignition timing. Therefore, both the above-described combustion stability and stall limit torque are always satisfied.

  According to the present invention, stable combustion can be obtained in a state where the ignition timing is significantly retarded from the compression top dead center. For example, when the internal combustion engine is cold, the exhaust gas temperature is raised and the catalyst is accelerated. Activation can be achieved and HC emissions can be reduced. By setting the ignition timing according to the engine temperature, the ignition timing can be sufficiently retarded while ensuring the combustion stability and the torque exceeding the stall limit torque, for example, combustion instability at extremely low temperatures. It is possible to avoid engine stoppage due to complications and friction.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  5 to 7 show an embodiment of a direct injection type spark ignition internal combustion engine to which the present invention is applied. In particular, FIGS. 5 and 6 show the configuration of one cylinder. Indicates the system configuration of the entire organization.

  As shown in FIGS. 5 and 6, a piston 3 is slidably disposed in a cylinder 2 formed in the cylinder block 1, and a cylinder head 4 fixed to the upper surface of the cylinder block 1 and the piston 3 A combustion chamber 5 is formed between them. The cylinder head 4 is formed with an intake port 7 that is opened and closed by an intake valve 6 and an exhaust port 9 that is opened and closed by an exhaust valve 8. A pair of intake valves 6 and a pair of exhaust valves 8 are provided for one cylinder, and an ignition plug 10 is disposed at the center of the ceiling surface of the combustion chamber 5 surrounded by these four valves. . Further, in this embodiment, a partition wall 11 is provided in the intake port 7 so as to partition the intake port 7 into two upper and lower flow paths so that the tumble flow can be strengthened depending on the operation state. A tumble control valve 12 that opens and closes the lower flow path at the upstream end is provided. As can be easily understood by those skilled in the art, the tumble flow is strengthened when the lower flow path is closed by the tumble control valve 12, and the tumble flow is weakened when the tumble control valve 12 is opened. The tumble control valve 12 is not necessarily essential in the present invention, and can be omitted. Alternatively, a known swirl control valve may be provided.

  A fuel injection valve 15 for directly injecting fuel into the cylinder is disposed below the intake port 7 of the cylinder head 4, more specifically at a position between the pair of intake ports 7. That is, the fuel injection valve 15 is located on the side of the combustion chamber 5 on the intake valve 6 side, and is arranged so as to inject fuel along a direction orthogonal to a piston pin (not shown) on the plan view. In the cross-sectional view of FIG. However, the downward inclination angle is relatively small, that is, the fuel is injected in a direction close to the horizontal.

  On the other hand, the top of the piston 3 has a convex shape along the inclination of the ceiling surface of the combustion chamber 5 that forms a pent roof type, and a concave portion 16 having a substantially rectangular shape in plan view is formed at the center. Yes. The bottom surface of the recess 16 forms an arc surface having a predetermined radius of curvature or a curved surface approximating an arc so as to follow the tumble flow.

  As shown in FIG. 7, the internal combustion engine of this embodiment is, for example, an in-line four-cylinder engine, and a catalytic converter 22 for purifying exhaust gas is provided in an exhaust passage 21 to which an exhaust port 9 of each cylinder is connected. An air-fuel ratio sensor 23 such as an oxygen sensor is disposed on the upstream side. The intake passage 24 to which the intake port 7 of each cylinder is connected is provided with an electronically controlled throttle valve 25 that is opened and closed by a control signal on the inlet side. An exhaust gas recirculation passage 26 is provided between the exhaust passage 21 and the intake air passage 24, and an exhaust gas recirculation control valve 27 is interposed in the middle. Further, the tumble control valves 12 of the respective cylinders are configured to be simultaneously opened and closed by a negative pressure type tumble control actuator 29 that is operated by a suction negative pressure introduced via a solenoid valve 28.

  The fuel injection valve 15 is supplied with the fuel adjusted to a predetermined pressure by the fuel pump 31 and the pressure regulator 32 via the fuel gallery 33. Therefore, when the fuel injection valve 15 of each cylinder is opened by the control pulse, an amount of fuel corresponding to the valve opening period is injected. In this embodiment, the fuel pressure is always kept constant. The ignition plug 10 of each cylinder is connected to an ignition coil 34.

  The fuel injection timing, injection amount, injection rate, ignition timing, and the like of the internal combustion engine are controlled by the control unit 35. The control unit 35 includes a detection signal of an accelerator opening sensor 30 that detects the amount of depression of an accelerator pedal, a detection signal of a crank angle sensor 36, a detection signal of an air-fuel ratio sensor 23, and a detection of a water temperature sensor 37 that detects a cooling water temperature. Signals, etc. are input.

  In the internal combustion engine configured as described above, when the warm-up is completed, for example, when the cooling water temperature exceeds 80 ° C., normal stratified combustion operation and homogeneous combustion operation are performed.

  That is, in a predetermined region on the low speed and low load side, as a normal stratified combustion operation mode, fuel injection is performed at an appropriate time in the compression stroke, with the tumble control valve 12 basically closed. Ignition is performed before the top dead center. In this operation mode, fuel injection always ends before compression top dead center. The fuel injected toward the piston 3 during the compression stroke is collected in the vicinity of the spark plug 10 using a tumble flow swirling along the recess 16 and ignited there. Therefore, stratified combustion with an average air-fuel ratio lean is realized.

  Further, in a predetermined region on the high speed and high load side after the warm-up is completed, fuel injection is performed during the intake stroke under the condition that the tumble control valve 12 is basically opened as a normal homogeneous combustion operation mode. And ignition is performed at the MBT point before the compression top dead center. In this case, the fuel becomes a homogeneous air-fuel mixture in the cylinder and is basically operated near the stoichiometric air-fuel ratio.

  On the other hand, when the cooling water temperature of the internal combustion engine is 80 ° C. or lower, that is, when the warm-up is not completed, the top dead center is used to activate the catalytic converter 22, that is, promote the temperature rise and reduce the HC emission amount. It becomes the injection operation mode. Then, as shown in FIG. 1 described above, the injection start timing ITS is before the compression top dead center (TDC), and the injection end timing ITE is after the compression top dead center (TDC). Is done. The ignition timing ADV is after compression top dead center (TDC), and is ignited at a timing delayed by 10 ° CA to 25 ° CA from the injection start timing ITS. During this delay period, the fuel spray just reaches the vicinity of the spark plug 10 and forms a combustible air-fuel mixture in the vicinity of the spark plug 10, so that ignition combustion is surely performed and stratified combustion is performed. At this time, the fuel injection amount is controlled so that the average air-fuel ratio becomes the stoichiometric air-fuel ratio.

  In this embodiment, the fuel injection timing is controlled so that the injection start timing ITS becomes a predetermined crank angle, and the injection end timing ITE is determined by the injection start timing ITS and the fuel injection amount (injection time). .

  As described above, the field in the combustion chamber near the compression top dead center where fuel is injected in this top dead center injection operation mode does not have a large flow that causes the spray to move due to the collapse of the large flow, Along with the collapse of the large flow, there are many minute disturbances that activate the combustion, and the field becomes very stable against the movement of the piston. Therefore, stable combustion is possible with the ignition timing retarded from the compression top dead center, and the retard limit of the ignition timing that is limited in terms of combustion stability is on the retard side. For this reason, the exhaust gas temperature can be significantly increased by a large retardation of the ignition timing, and the HC emission amount is reduced.

  Here, the ignition timing and the fuel injection timing in the top dead center injection operation mode are further corrected based on the engine temperature, for example, the coolant temperature.

  FIG. 8 is a flowchart showing an outline of the control. First, in step 1, it is determined whether or not the exhaust gas temperature needs to be increased, that is, whether or not the top dead center injection operation mode is required. YES If so, the process proceeds to step 2 and the top dead center injection operation mode is executed. As described above, for example, if the cooling water temperature exceeds 80 ° C., this routine ends, and a normal stratified combustion operation or homogeneous combustion operation is performed. In step 2, the first ignition timing (ignition timing A) determined so that the combustion stability is equal to or higher than the predetermined combustion stability, and the generated torque are determined to overcome the friction and maintain the autonomous operation. The second ignition timing (ignition timing B) is calculated. These ignition timings A and B are basically determined based on the coolant temperature. Then, in step 3, the two are compared, and one of the values on the advance side is set as the ignition timing in step 4. In step 5, the fuel injection timing (fuel injection start timing ITS) is calculated and determined based on the final ignition timing or cooling water temperature. Note that the coolant temperature gradually rises after the start, so the coolant temperature may be repeatedly detected and the optimum ignition timing and fuel injection start timing may be obtained sequentially, but top dead center for simplification of control. The initial ignition timing and fuel injection start timing are set based on the cooling water temperature at the start of the injection operation mode (generally the cooling water temperature at the engine start), and this initial value is changed during the continuation of the top dead center injection operation mode. You may make it use without.

  FIG. 9 shows the relationship between the combustion stability and the ignition timing, and a line L1 in the figure shows an example of characteristics under a certain cooling water temperature (engine temperature). As shown in the figure, the combustion stability decreases as the ignition timing is retarded, and cannot be retarded beyond a predetermined stability limit. Therefore, the first ignition timing (ignition timing A) under a certain coolant temperature is determined by the intersection of the line L1 and the line indicating the stability limit. When the cooling water temperature is different, the characteristic indicated by the line L1 changes. For example, when the cooling water temperature is low, the combustion stability is lower (upward in FIG. 9) for the same ignition timing. Therefore, the first ignition timing (ignition timing A) basically has characteristics as shown in FIG. 10 with respect to the coolant temperature. In step 2 described above, the ignition timing A is basically obtained based on the cooling water temperature. However, the ignition timing is also considered in consideration of other parameters other than the cooling water temperature that affect the combustion stability, such as the outside air temperature. More preferably, A is determined.

  On the other hand, FIG. 11 shows the relationship between the generated torque of the engine and the ignition timing, and the line Tf in the figure can overcome the friction of each part of the engine under a certain cooling water temperature (engine temperature) and can operate independently. The minimum torque (stall limit torque) is shown. The engine generated torque decreases as the ignition timing is retarded, as shown by line L2. Therefore, the second ignition timing (ignition timing B) under a certain cooling water temperature is determined by the intersection of the line L2 and the line Tf, and if it is delayed more than this, a stall may occur due to friction. is there. Since the friction (mechanical loss) of each part of the engine increases as the coolant temperature decreases as shown in the upper part of FIG. 12, the stall limit torque Tf increases as the temperature decreases. The value of the ignition timing (ignition timing B) is on the advance side. Therefore, the second ignition timing (ignition timing B) basically has characteristics as shown in the lower part of FIG. 12 with respect to the coolant temperature. In step 2 described above, the ignition timing B is basically obtained based on the coolant temperature. However, the ignition timing B is determined in consideration of the ON / OFF state of the auxiliary equipment involved in the friction of the entire engine. It is more preferable to do.

  In steps 3 and 4 described above, since the advance side is selected in the ignition timings A and B, as is apparent from FIGS. The requirement from the viewpoint of torque is satisfied at the same time, and even when the temperature is extremely low, combustion instability and stall do not occur.

  Further, the fuel injection start timing is set with the characteristics shown in FIG. 13 with respect to the coolant temperature. That is, the fuel injection start timing is corrected to the advance side as the coolant temperature is lower. Therefore, even if the ignition timing is delayed according to the coolant temperature, an appropriate delay period is ensured from the fuel injection start timing to the ignition timing, so that the fuel spray just reaches the vicinity of the spark plug 10 and near the spark plug 10. When the combustible air-fuel mixture is formed, ignition is performed, and reliable ignition can be ensured. The fuel injection start timing may be determined based on the ignition timing determined in step 4.

  As mentioned above, although one Example of this invention was described, this invention is not limited to the said Example, A various change is possible. In the above embodiment, both the ignition timings A and B are obtained and the advance side is selected. However, for the sake of simplification of the control, the ignition timing A or the ignition timing A calculated according to the cooling water temperature is selected. The ignition timing B may be set as the final ignition timing as it is.

The characteristic view which showed an example of the fuel-injection period and ignition timing of this invention. The characteristic figure of the piston position change amount and volume change amount during a cycle. The characteristic figure which shows the change in the cycle of a big flow. The characteristic view which shows the change in the cycle of a minute disturbance. Sectional drawing which shows one Example of a direct injection type spark ignition internal combustion engine. FIG. FIG. 2 is a configuration explanatory view showing the system configuration of the entire internal combustion engine. The flowchart which shows the outline of control. The characteristic view which shows the relationship between combustion stability and ignition timing. The characteristic view which shows the characteristic of the ignition timing A with respect to cooling water temperature. The characteristic view which shows the relationship between generated torque and ignition timing. The characteristic view which shows the characteristic of the mechanical loss and the ignition timing B with respect to cooling water temperature. The characteristic view which shows the characteristic of the fuel injection timing with respect to cooling water temperature.

Explanation of symbols

3 ... Piston 5 ... Combustion chamber 10 ... Spark plug 15 ... Fuel injection valve

Claims (5)

  In a control device for a direct injection type spark ignition internal combustion engine having a fuel injection valve for directly injecting fuel into a cylinder and having an ignition plug, the top dead center injection operation mode is set in a predetermined operating state. , Fuel injection is performed in a period straddling the compression top dead center such that the injection start time is before the compression top dead center and the injection end time is after the compression top dead center, and the compression top dead is delayed from the injection start time. An in-cylinder direct injection spark ignition internal combustion engine control device characterized in that ignition is performed after a point and the ignition timing is set according to the engine temperature.   2. The control device for an in-cylinder direct injection spark ignition internal combustion engine according to claim 1, wherein the ignition timing is set according to the engine temperature so that the combustion stability is equal to or higher than a predetermined combustion stability.   2. The control apparatus for a direct injection spark ignition internal combustion engine according to claim 1, wherein the ignition timing is set in accordance with the engine temperature so that the generated torque exceeds a stall limit torque that varies with temperature. .   The first ignition timing determined according to the engine temperature and the generated torque so that the combustion stability is equal to or higher than the predetermined combustion stability and the stall limit torque that varies depending on the temperature. 2. The control apparatus for a direct injection spark-ignition internal combustion engine according to claim 1, wherein the second ignition timing obtained is compared and an advance value is set as the ignition timing. The in-cylinder direct injection type according to any one of claims 1 to 4, wherein the top dead center injection operation mode is executed when a rise in exhaust gas temperature is required as a predetermined operation state. Control device for spark ignition internal combustion engine.

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